FIG. 2.

The pMycoPuro plasmid confers puromycin resistance. M. capricolum was grown in SP4 medium with a range of puromycin concentrations in the presence or absence of the pMycoPuro plasmid. Without the plasmid, M. capricolum grew slowly at a puromycin concentration of 1.2 μg/ml and no growth was observed at 3.7 μg/ml. In this color-changing unit assay, the change of the pH indicator phenol red in the medium from red to yellow was used as an indicator of growth. In the absence of cell growth, the SP4 medium does not change color over the time course of the experiment (24 h). M. capricolum cells containing the vector were resistant to puromycin at concentrations of at least 300 μg/ml.